Current transformer



July 8, 1969 JEANMAR[E E P ETAL 3,454,915

CURRENT TRANSFORMER Filed Dec. 19, 1967 United States Patent Office 3,454,915 CURRENT TRANSFORMER Jean-Marie Derippe and Pierre Maurice Aumont, Aix-les- Bains, France, assignors to 'Alsthom-Savoisienne, Saint- Ouen, France, a corporation of France Filed Dec. 19, 1967, Ser. No. 691,732 Claims priority, applicatipn France, Dec. 22, 1966,

Int. or. from 27/08 US. Cl. 336-60 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a current transformer and more particularly to current transformers which are cooled by liquid dielectrics.

customarily, the insulation for the primary winding of current transformers usually consists of insulating layers around the primary loop. These insulating layers may be of paper, preferably impregnated by a dielectric liquid. It is customary to provide thin conductive layers within the insulation in order to provide equal potential surfaces and for even distribution of the potential gradient. These insulating layers, to insulate the primary from the secondary sensing windings, pose cooling problems, particularly when the transformers are used in connection with extremely high voltage lines.

It has been proposed to provide longitudinal channels or ducts between the insulating layers in order to permit circulation of dielectric fluid and thus to serve as a cooling medium for the winding. Providing ducts in the interior of the inulsation of transformers in which the windings form a single loop, the ends of which are extensions of conductors having vertical terminal portions, permits decreasing the thickness of the insulating material, and further facilitates its drying and impregnation. However, it is difficult to obtain .a natural fluid circulation, that is circulation due to thermal effects, if these channels or ducts should follow equal equipotential lines so that at their ends, they will terminate at the same level in the chamber formed by the current transformer housing or the insulating" material insulating the output conductors and the exterior of the transformer.

'It is an object of the pesent invention to provide a current transformer having a loop-type primary in which natural circulation of the dielectric fluid can be obtained, due to thermal effects.

Subject matter of the invention.The current transformer according to the invention is so arranged that channels are formed within the insulation next to the entrance and exit conductors, which channels extend towards the top of the transformer assembly, within the outside insulator, in order to extend the internal ducts in the region of the transformer winding loop upwardly to provide a thermosyphon action and thus for fluid circulation within the insulation.

The structure, organization, and operation of the invention will now be described more specifically with reference to the accompanying drawings, wherein:

FIG. 1 is a vertical cross sectional view of a current transformer, both the secondary Winding as well as the Patented July 8, 1969 magnetic circuit having been omitted for purposes of clarity; and

FIG. 2 is a sectional view along lines IIII of FIG. 1.

Referring now to the drawings: The primary winding is a single loop 1, and is connected by vertical extensions 2 to input and output terminals 3 and 4 secured to a terminal head 5.

A metallic wall 6, covered by electrical insulation 7 is disposed around the Winding. The insulation 7 has electrically conductive layers 8 inserted therein in order to form equal potential surfaces to distribute the electrostatic gradients. The whole assembly is bathed in a dielectric fluid contained within a housing or vessel 9, and extending into the interior of the outside insulator 10, which interconnects the housing 9 and the terminal head 5. The fluid also extends within terminal head 5.

A duct, or channel 11 is formed in the insulation 7, which separates the insulating material into two parts. This duct may, for example, be formed with longitudinal inserts, not shonw in FIG. 1, and forming a free space between two adjacent insulating layers, thus forming a number of duct elements longitudinally extending and further extending along the vertical portion 12 of the insulation. These ducts communicte with the lower, toroidal portion 13. The duct is preferably close to a layer 8. The upper terminals of these ducts end at the cylindrical side 12 of the insulation, as seen at 14 on the left-hand side of the drawings, and at 15 at the right-hand side of the drawings.

Half of the circumference at the right-hand side of the cylindrical insulation portion 12 has an insulating envelope 16 attached thereto, in general form of two half-cylinders, and extending towards the top of the transformer from the orifice 15 of the duct 11, to form a conduit 17, closed at the lower end to the insulation and starting at the orifice 15, in order to extend the channel or duct 11 towards the top of the transformer. This outer mantle 16 may, for example, be of paper or cardboard, impregnated with dielectric substance. It may be adhered to the insulation 7. Alternatively, the mantle 16 may be secured to the insulation 7 by a small flange and a ribbon of insulating substance around the flange and insulation 7, by clamps, or other suitable means. Heat arising due to dielectric loss in the insulation causes natural circulation, by thermal syphon effect of the dielectric fluid in channel 11. The fluid may enter the free orifice 14, seen at the left-hand side of the drawings, circulate around duct 11 and leave by the higher effective end of the duct at the right-hand side, formed by the mantle extension 16.

Various changes or modifications may be made, within the inventive concept, to suit particular design requirements and the described embodiment is intended to illustrate the inventive concept only.

We claim:

1. Current transformer having a housing, an insulator mounted above said housing and a terminal head above said insulator, said housing, insulator and terminal head forming a hollow assembly and confining a dielectric fluid therein;

a loop primary winding located at a lower portion of the transformer and within said housing, and vertically extending lead conductors, extending through said insulator upwardly into said terminal head;

insulation material covering said primary winding and insulating said primary winding against ground, and forming a lower loop portion and upwardly extending portions surrounding said loop primary winding and said lead conductors, respectively;

at least one duct formed within said insulation material in the region between said primary winding and the outside of said insulation material to provide a duct having walls formed entirely of insulation material, said duct having a first portion extending within said insulating material at least in part parallel to said vertically extending lead conductor, a second portion extending around said loop portion and a third portion again at least in part parallel to said vertically extending lead conductor, said first and third portions having terminal openings" in said upwardly extending portions of the insulation, one terminal opening of said duct portions being at a higher elevation that the other terminal opening of the other duct portion.

2. Transformer according to claim 1 wherein said first and third duct portions are symmetrically arranged at opposite sides within said insulation material;

and an upwardly extending mantle connects with one of said terminal openings to effectively extend the duct portion'on one side of said transformer to a higher level than the duct portion on the other side, thus providing for thermal-syphon action to circulate fluid disposed within said hollow assembly.

3. Transformer according to claim 1, including an upwardly extending mantle connecting with said third duct portion and located at the outside of the insulation ma- 4 terial to extend said third duct portion to a higher level than the first duct portion, and providing for thermalsyphon action to circulate fluid disposed within said insulation material.

4. Transformer according to claim 1, including layers of conductive material located within said insulation material close to said duct to provide for equal potentia surfaces therein.

5. Transformer according to claim 3, including layers of conductive material located with said insulation mate'- rial close to said duct to provide for equal potential surfaces therein.

References Cited UNITED STATES PATENTS 3,173,114 3/1965 Peuron 33684 3,201,728 8/1965 McWhirter 33660 3,299,383 1/1967 Conner et al. 33660 LEWIS H. MYERS, Primary Examiner.

T. J. KOZMA, Assistant Examiner. 

